a. Field of the Invention
This invention relates to methods for pattern bonding nonwoven webs made from polyamide filaments.
B. Description of the Prior Art
Various methods of bonding nonwoven webs are known. For example, U.S. Pat. No. 3,647,591 discloses a process for bonding the entire area of a nonwoven web made up of a blend of nylon fibers and fibers of another kind which are not affected by a strong acid such as hydrochloric acid. The acid is applied to the web from an aqueous solution by spraying or dipping, with the fabric then being hot calendered to bond the nylon filaments in the web together. Under these conditions, the acid dissolves the nylon filaments so that these filaments more or less serve as an adhesive which bonds the filaments in the web together, the other filaments in the web providing strength.
U.S. Pat. No. 3,676,244 to Kim discloses a process for bonding the entire area of a web made from polyamide filaments wherein the web is passed through a preconditioning zone such that the web picks up from 3 to 6 weight percent of water, with the web then being passed through a second zone where the web absorbs a hydrogen halide gas and additional moisture. The purpose of the preconditioning step is to allow the web to pick up the gas at a higher rate. The web is then self-bonded by washing it in water at room temperature to remove the absorbed gas.
U.S. Pat. No. 3,516,900 to Mallonee et al discloses a process for bonding the entire area of a polyamide nonwoven fabric by exposing the fabric to gaseous hydrogen halide or boron trifluoride and then removing the activating gas from the fabric by either washing at room temperature or heating.
Nonwoven fabrics which are bonded over the entire fabric area have poor drapability and are usually stiff and papery. Such nonwoven fabrics are unsuited for many end uses where the physical characteristics of a conventional fabric are required. It is known that nonwoven fabrics have better drape and hand if only spaced, discrete areas of the fabric are bonded. This fabric is made by a process known as "pattern bonding".
In some pattern bonding processes the bonding is achieved by the application of an adhesive to discrete, spaced areas of the fabric. Disadvantages of this process are that a foreign material is introduced into the fabric and it is difficult to control lateral migration of the adhesive while achieving penetration of the web. Also, adhesive buildup on the process equipment may be a problem.
In another pattern bonding method the nonwoven fabric is pressed between a pair of rolls, at least one of which is embossed and heated to such a temperature that, in discrete areas of the fabric, roll pressure and heat compacts and melts the fibers of the web together. Unfortunately, as in U.S. Pat. No. 3,855,045, when the roll is hot enough to assure a strong bond in the bonded area, a certain amount of bonding will occur in the remainder of the fabric. Thus, the drape and hand of the fabric will be somewhat impaired. Some of the bonds in the uncompacted area of the fabric can be broken by working the fabric, but this adds another step to the process.
Ideally, the pattern bonded fabric will have discrete bonded areas with little or no bonding in the remainder of the fabric. Such a fabric will have a high tenacity but will still have good drape and hand.